In the mobile communication system, in order to guarantee the service quality and provide excellent service experience for users, after user equipment (UE) establishes connection with the internet in a certain cell, the UE still needs to measure the signal qualities of the service cell and neighboring cells and select appropriate cell to perform the switching so that the mobility requirements can be met.
FIG. 1 is a schematic drawing of the switching process of X2 interface according to correlative technology. As shown in FIG. 1, in the long term evolution (LTE) system, the switching process of the X2 interface comprises the steps as follows:
Step 101, the source base station sends a measurement control message to the UE in connecting state;
Step 102, the UE executes the measurement and submits the measurement report;
Step 103, the source base station determines to perform the switching and selects the target cell according to the received measurement report and in connection with practical situations;
Step 104, the source base station sends a switching request message to the target base station to which the target cell belongs, wherein the switching request message carries the capability information of the UE, the configuration information of an application server (AS) layer, radio resource management (RRM) configuration information, and context information;
Step 105, after performing resource reservation processing, the target base station responds a switching request response message to the resource base station, wherein the switching request response message carries the switching command information to the UE. The switching command information comprises the target cell information (the target cell can be different from the target cell in the switching request message);
Step 106, the source base station sends the switching command (namely RRC reconfiguration) to the UE;
Step 107, after completing the random access into the target cell, the UE sends a switching completion command to the target base station.
The switching process of S1 interface is similar to the switching process of the X2 interface except that the intercommunicating messages during the switching are forwarded by the MME.
The main basis that the source base station makes the switching decision is the measurement result. In the LTE system in connecting state, the specific measurement process is as follows: the network side sends the measurement control message to the UE, wherein the measurement control message carries measurement identification (MID), measurement object (MO), report configuration (RC) and the other measurement relative attributes. The measurement identification correlates the MO to the RC to form an entire measurement task. The MO comprises the attributes (e.g. carrier, neighboring cells list etc.) of the measurement object. Each carrier is configured with only one measurement object. The RC comprises the attributes (e.g. event activating or periodic reporting, definitions (A1, A2 . . . ) of the activated events, reporting times etc.) of the report configuration. The UE executes the measurement and evaluation according to the MO and RC in the measurement control message, generates a measurement report according to the measurement result, and submits the measurement report to the network side. The network side decides whether to perform the switching according to the measurement report submitted by the UE.
In the LTE, some key mobility parameters can be negotiated between the base stations (called as base station 1 and base station 2 hereafter). FIG. 2 is a schematic drawing of mobility parameters negotiation process according to correlative technology. The mobility parameters negotiation is realized through the steps as follows: the base station 1 sends a mobility parameter change request to the base station 2; if the base station 2 accepts the change, the base station 2 responds a mobility parameter change response to the base station 1.
FIG. 3 is a schematic drawing of X2 interface setup process between the base stations according to correlative technology. As shown in FIG. 3, the base station sends an X2 setup request to the base station 2; and base station 2 responds an X2 setup response to the base station 1.
In order to provides higher data rate for mobile users, the long term evolution advance (LET-A) system puts forward a carrier aggregation (CA) technology, with the purpose to provide wider broad band for the UE with corresponding abilities and improve the peak rate of the UE. In the LTE, the maximum downlink transmission bandwidth supported by the system is 20 MHz. The CA refers to the technology which aggregates two or a plurality of component carriers (CC) to support the transmission bandwidths more than 20 MHz and not more than 100 MHz to the maximum. The LTE-A UE with the carrier aggregation ability can send and receive data in a plurality of component carriers. The UE mentioned hereafter refers to the LTE-A UE with the carrier aggregation ability except in exceptional circumstances. In the LTE-A system, after entering the connecting state, the UE can communicate with the source base station through a plurality of component carriers (e.g. CC1, CC2) at the same time. The base station will designate a primary component carrier (PCC) through explicit configuration or according to protocol agreement, and the other component carriers are called as secondary component carriers (SCC). The service cell on the DL PCC is called as primary cell (Pcell), and the service cell on the DL SCC is called as secondary cell (Scell).
The switching process in the LTE-A is the same with the switching process in the LTE. The source base station sends the measurement control message to the UE in connecting state; the UE executes the measurement and submits the measurement report; the source base station determines to perform the switching and selects the target Pcell according to the received measurement report and in connection with practical situations; the source base station sends the switching request message to the target base station to which the target Pcell belongs, wherein the switching request message carries the capability information of the UE, the configuration information of the AS layer, the RRM configuration information, and context information; after performing resource reservation processing, the target base station responds the switching request response message to the resource base station, wherein the switching request response message carries the switching command information to the UE; the switching command information comprises the target Pcell information (the target Pcell can be different from the target Pcell in the switching request message), and can also comprise one or a plurality of Scells; the UE receives the switching command (namely RRC reconfiguration) from the source base station; after completing the random access into the target Pcell, the UE sends the switching completion command to the target base station.
In order to cooperate with the target base station to configure one or a plurality of Scells, the switching request message sent to the target base station by the source base station also carries an optimum cell list, and the signal quality of the cells (e.g. reference signal received power (RSRP) and reference signal received quality (RSRQ)). The cells in the list are non-service cells which are sequenced in descending order according to wireless signal quality (that is to say, the optimum cell is sequenced at the foremost). Aiming at each frequency, the source base station selects at least one optimum cell from the available measurement report to form the optimum cell list. The target base station can configure the Scell for the UE according the list. As a matter of course, the configured Scell can be not the cells in the list.
As seen in the above-mentioned description, in correlative technologies, after completing the decision-making process of cell switching, the source base station transmits the signal quality of the backup Scells to the target base station through the optimum cell list which provides basis for the target base station to select Scells. However, in the present processing mode, the target base station can only acquire the signal quality of the backup Scells notified by the source base station, or the cells in the optimum cell list are comparatively unorganized, with the result that the judgment accuracy of the Scells is influenced and the processing complexity of the target base station is increased.